1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and to a method of manufacturing such a magnetic head.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in the direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared with the longitudinal magnetic recording system.
Typically, magnetic heads for perpendicular magnetic recording have a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter referred to as an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate, like magnetic heads for longitudinal magnetic recording. The write head includes a pole layer that generates a magnetic field in the direction perpendicular to the plane of the recording medium. The pole layer includes, for example, a track width defining portion having an end located in a medium facing surface that faces toward the recording medium, and a wide portion that is coupled to the other end of the track width defining portion and that is greater in width than the track width defining portion. The track width defining portion has a nearly uniform width.
For the perpendicular magnetic recording system, it is an improvement in recording medium and an improvement in write head that mainly contributes to an improvement in recording density. It is a reduction in track width and an improvement in write characteristics that is particularly required for the write head to achieve higher recording density. On the other hand, if the track width is reduced, the write characteristics, such as an overwrite property that is a parameter indicating an overwriting capability, suffer degradation. It is therefore required to achieve better write characteristics as the track width becomes smaller. Here, the length of the track width defining portion taken in the direction perpendicular to the medium facing surface is called a neck height. The smaller the neck height, the better is the overwrite property.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider is designed to slightly fly over the surface of the recording medium by means of an airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive, the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs in accordance with the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system, in particular, which exhibits a better capability of writing on a recording medium compared with the longitudinal magnetic recording system, if the above-mentioned skew occurs, there arise problems such as a phenomenon in which, when data is written on a certain track, data stored on a track adjacent thereto is erased (this is hereinafter called adjacent track erasing), or unwanted writing between two adjacent tracks. To achieve higher recording density, it is required to suppress adjacent track erasing. Unwanted writing between two adjacent tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of a read signal.
As one of techniques for preventing the problems resulting from the skew described above, there is known a technique in which an end face of the track width defining portion located in the medium facing surface is formed into such a shape that the side located backward along the direction of travel of the recording medium (that is, the side located closer to the air inflow end of the slider) is shorter than the opposite side, as disclosed in U.S. Patent Application Publication No. US 2003/0151850 A1, for example. For magnetic heads, typically, in the medium facing surface, the end farther from the substrate is located forward along the direction of travel of the recording medium (that is, located closer to the air outflow end of the slider). Therefore, the shape of the end face of the track width defining portion located in the medium facing surface mentioned above is such that the side closer to the substrate is shorter than the side farther from the substrate.
U.S. Patent Application Publication No. 2003/0151850 A1 discloses a process of forming a groove having a shape corresponding to the pole layer in an inorganic insulating film, and forming the pole layer in the groove by plating or sputtering. According to this process, the width of the pole layer, that is, the track width, is defined by the width of the groove formed in the inorganic insulating film. This U.S. publication further discloses that, when the pole layer is formed in the groove by plating, a stopper film used for CMP may be formed after the plating base film is formed.
U.S. Patent Application Publication No. US 2006/0077589 A1 discloses a method of forming the pole layer as described below. In this method, first, a polishing stopper layer having a penetrating opening whose shape corresponds to the plane geometry of the pole layer is formed on the top surface of a nonmagnetic layer. Next, a portion of the nonmagnetic layer exposed from the opening of the polishing stopper layer is selectively etched to thereby form a groove in the nonmagnetic layer, and a magnetic layer to become the pole layer is formed such that the groove is filled with the magnetic layer and that the top surface of the magnetic layer is located higher than the top surface of the polishing stopper layer. Next, a coating layer is formed to cover the magnetic layer and the polishing stopper layer. Next, the coating layer and the magnetic layer are polished until the polishing stopper layer is exposed, so that the magnetic layer becomes the pole layer. This method makes it possible to precisely control the thickness of the pole layer that has an influence on the write characteristics, and the width of the top surface of the pole layer that defines the track width.
One of approaches for improving write characteristics is to form the pole layer using a magnetic material having a high saturation flux density. For example, CoFe is one of magnetic materials having a high saturation flux density. On the other hand, it is known that a magnetic layer formed by physical vapor deposition such as sputtering may have a higher saturation flux density compared with a magnetic layer formed by plating. For example, a CoFe layer formed by plating has a saturation flux density of approximately 2.3 T, whereas a CoFe layer formed by physical vapor deposition has a saturation flux density of approximately 2.4 T.
In view of this, forming a CoFe layer to become the pole layer by physical vapor deposition in a groove of a nonmagnetic layer would be a possible approach for improving the write characteristics and also precisely controlling the write characteristics and the track width.
On the other hand, to achieve higher recording density, a reduction in track width is required, and to achieve this, it is necessary to reduce the width of the above-mentioned groove. When the pole layer is formed in a narrow groove by physical vapor deposition, however, there arise a problem that defects such as key holes can easily occur in the pole layer.
Furthermore, forming the pole layer in a groove by physical vapor deposition can sometimes include a process in which a thin seed layer made of a nonmagnetic metal material or a magnetic material is first formed in the groove by sputtering, and then a thick magnetic layer is formed on this seed layer by physical vapor deposition. In this case, the surface of the seed layer formed in the groove becomes a rough surface on which a columnar crystal appears. Consequently, if a magnetic layer is formed on this seed layer by physical vapor deposition, the magnetic layer is poor in quality of the crystal, and this results in degradation in characteristics of the pole layer.
In the case of forming the pole layer by plating in a narrow groove, there also arise a problem as described below. To form the pole layer in a groove by plating, typically, a thin seed layer made of a nonmagnetic metal material or a magnetic material is first formed in the groove by sputtering, for example, and then a plating layer made of a magnetic material is formed on the seed layer by plating. In this case, as mentioned above, the surface of the seed layer formed in the groove becomes a rough surface on which a columnar crystal appears. Consequently, if a plating layer is formed on this seed layer, the plating layer is poor in quality of the crystal, and this results in degradation in characteristics of the pole layer.